The present invention relates to a multilayer ceramic capacitor having dielectric layers and conducting layers laminated alternately and a manufacturing method thereof; and, more particularly, to a structure of a dielectric ceramic layer of a multilayer ceramic capacitor.
Multilayer ceramic capacitors are normally manufactured by first mixing a dielectric ceramic powder such as BaTiO3 with additives and a binder and then stirring the mixture using, for example, a ball mill for several hours, thereby obtaining a slurry having a preferable viscosity.
Next, ceramic green sheets are made out of the slurry by using, for example, a doctor blade method and the like. In the doctor blade method, the slurry is cast onto a base film and dried thereon to thereby form a ceramic green sheet having a predetermined thickness. The thickness of the ceramic green sheet is controlled by adjusting a gap between the base film and a doctor blade.
Then, a conductive paste is printed in a predetermined pattern on the ceramic green sheet. Thereafter, a number of the ceramic green sheets are laminated and pressed, thereby forming an unsintered laminated body. The unsintered laminated body is diced into a plurality of green chips and the green chips are sintered. During the sintering, the ceramic green sheets are turned into dielectric layers and the conductive paste is turned into conductive layers. Finally, a conductive paste is coated on the sintered chips, which becomes external electrodes in finished products.
In such a multilayer ceramic capacitor, delamination or crack generation remains as problems to be solved. One of the causes of delamination stems from a difference between the shrinkage rate of the ceramic green sheet and that of the conductive paste during the sintering. In a generally adopted method for preventing delamination, the dielectric ceramic powder, which is used to form the ceramic green sheet, is added into the conductive paste. The dielectric ceramic powder added into the conductive paste for preventing delamination is referred to as xe2x80x9ccommon materialxe2x80x9d.
However, as the thickness of each dielectric layer of the multilayer ceramic capacitor becomes smaller to meet the requirement for higher capacity and smaller size, changes in the characteristics of the dielectric layers by diffusion of the common material thereinto may become significant.
It is, therefore, an object of the present invention to provide a multilayer ceramic capacitor having a preferable voltage withstand characteristic and being capable of accomplishing a higher capacitance and smaller size.
In accordance with one aspect of the present invention, there is provided a multilayer ceramic capacitor comprising dielectric ceramic layers and conductive layers, the dielectric ceramic layers including core-shell structured ceramic particles, wherein the ceramic particles disposed nearer to the conductive layers have shell portions having thicknesses larger than those of the ceramic particles disposed farther from the conductive layer.
As another aspect of the present invention, there is provided a manufacturing method of a multilayer ceramic capacitor which comprises the steps of preparing a slurry by mixing a first dielectric ceramic powder with a first additive and a binder, forming a ceramic green sheet by using the slurry, preparing a conductive paste by mixing a second dielectric ceramic powder with a second additive, the second additive including at least one component of the first additive, printing the conductive paste on the ceramic green sheet, forming a laminated body by laminating a plurality of the ceramic green sheets having the conductive paste printed thereon, and sintering the laminated body.